Afinitor Delays Breast Cancer Progression

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Among postmenopausal women with advanced breast cancer that had become resistant to hormonal therapy, the combination of Afinitor® (everolimus) and Aromasin® (exemestane) delayed cancer progression to a greater extent than Aromasin alone. The results of this Phase III clinical trial were presented at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium.

Each year roughly 200,000 U.S. women are diagnosed with breast cancer. Many of these breast cancers are hormone receptor-positive, meaning that exposure to estrogen and/or progesterone can cause them to grow.

Treatment of hormone receptor-positive breast cancer often includes hormonal therapies such as tamoxifen or an aromatase inhibitor. Tamoxifen acts by blocking estrogen receptors, and aromatase inhibitors suppress the production of estrogen in postmenopausal women. Aromatase inhibitors include Femara® (letrozole), Arimidex® (anastrozole), and Aromasin® (exemestane). Many women with advanced breast cancer become resistant to hormonal therapy, and treatment options for these women remain limited.

Afinitor is an oral medication that works by inhibiting a protein known as mTOR. The mTOR protein plays an important role in regulating cancer cell division and blood vessel growth. Currently, Afinitor is used for the treatment of selected patients with kidney cancer, pancreatic neuroendocrine tumors, and subependymal giant cell astrocytoma (SEGA).

To explore the use of Afinitor among women with advanced, estrogen receptor-positive, HER2-negative breast cancer, researchers conducted a Phase III clinical trial (BOLERO-2) among 724 women. All of the women had experienced cancer recurrence or progression in spite of treatment with Femara or Arimidex. Study participants were treated with Aromasin alone or in combination with Afinitor.

Survival without cancer progression was 7.4 months among women treated with both Afinitor and Aromasin, compared with 3.2 months among women treated with Aromasin alone.

The most common side effects in the Afinitor group were oral mucositis, fatigue, lung inflammation, and high blood sugar.

These results suggest that the addition of Afinitor to Aromasin improved outcomes among women with advanced breast cancer that had previously been treated with hormonal therapy. Afinitor has not yet been approved for use in breast cancer.